So, here's a super step-by-step explanation:
Ok, the back of the board looks like this. It tells you what to do to make different sized envelopes.
I selected 4 bar and cut my card stock down to the appropriate size listed on the back of the board with my paper trimmer.
Then, I lined up my card stock on the board so that the edges matched up to the dotted lines for the correct size envelope. (Feeling Like an Idiot Moment # 1: I initially cut the paper the wrong size by mistake and couldn't figure out why it wasn't fitting inside the lines.)
Then, I attempted to follow the directions and score the paper at the correct lines for a 4 bar sized envelope. I messed up. (Feeling Like an Idiot Moment # 2) I knew it wasn't right because the board said I should have creased triangles, and I did not.
Ok, I cut a new sheet of card stock and tried again. I don't think I was following the correct lines to score the first time. Use the lines with the arrows, guys. The arrows! Wow, I am easily confused.
Then, I cut out the creased triangles. (Feeling Like an Idiot Moment # 3: I didn't realize that there were 4 of these rather than 2 and couldn't figure out what was wrong.)
I folded the envelope on the score lines.
I applied adhesive to finish the construction process.
So, looking back, this was not complicated in the slightest, but there was just something about all the lines on the board that just threw me for an idiot loop (both in lacking confidence and in messing up). But, if I've learned anything from paper crafting, it's that you can always use a new piece of paper. It's okay to start over with a new piece of paper.
Update: Well after I had initially written this post, I saw this brilliant post from the Frugal Crafter where she illustrates a method she learned from a fellow artist to make an envelope any size without a template. We can do this, everyone! We can make paper to transport other paper from one place to another!